[issue20729] mailbox.Mailbox does odd hasattr() check

[Serhiy Storchaka]

Changes by Serhiy Storchaka :


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resolution:  -> fixed
stage: patch review -> resolved
status: open -> closed

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[issue20729] mailbox.Mailbox does odd hasattr() check

[Roundup Robot]

Roundup Robot added the comment:

New changeset 5fd1f8271e8a by Serhiy Storchaka in branch '3.4':
Issue #20729: Restored the use of lazy iterkeys()/itervalues()/iteritems()
http://hg.python.org/cpython/rev/5fd1f8271e8a

New changeset acb30ed7eceb by Serhiy Storchaka in branch 'default':
Issue #20729: Restored the use of lazy iterkeys()/itervalues()/iteritems()
http://hg.python.org/cpython/rev/acb30ed7eceb

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[issue20729] mailbox.Mailbox does odd hasattr() check

[R. David Murray]

R. David Murray added the comment:

Committing the patch seems like the right thing to do at this point in time.

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[issue20729] mailbox.Mailbox does odd hasattr() check

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

If there are no objections I'll commit this patch.

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assignee:  -> serhiy.storchaka
versions: +Python 3.5 -Python 3.3

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[issue20729] mailbox.Mailbox does odd hasattr() check

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

Note that there is a difference between Mailbox and dict interface: __iter__() 
iterates over values, not keys.

clear() should use keys(), not iterkeys(), because it modifies iterated dict.

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[issue20729] mailbox.Mailbox does odd hasattr() check

[Peter Otten]

Peter Otten added the comment:

Do you expect many use cases that rely on items(), keys(), and values() being 
lists? 
Maybe it would be acceptable to make these lazy in 3.5, but keep the iterXXX() 
variants as aliases indefinitely.

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[issue20729] mailbox.Mailbox does odd hasattr() check

[Terry J. Reedy]

Terry J. Reedy added the comment:

You have opened the door on a slight mess. The mailbox module provides a set + 
dict interface to on-disk mailbax files in various formats. The hg annotate and 
revision history commands indicate that most of 3.4 mailbox is unchanged since 
the trunk version was merged into py3k on 2006-5-27 in rev38453. However, on 
2007-2-11 Guido changed .iterxxx to .xxx throughout the stdlib in rev40809.

The bug you note is a side-effect of this patch. It overall left mailbax in a 
somewhat inconsistent state as it did *not* update the mailbox dict API by 
removing the mailbox.iterkeys/values/items methods and replacing the 
.keys/values/items methods. As a result, the mailbox methods that space 
efficiently iterated thru self.iterkeys now iterate through self.keys == 
list(self.iterkeys). Example:
def clear(self):
"""Delete all messages."""
for key in self.keys():  # was self.iterkeys()
self.discard(key)

To fix this, I think we should either
1) revert the rev40809 changes to mailbox, including in the line you point to, 
or
2) complete the rev40809 changes by updating to a Py3 interface, and make the 
change you suggest.

1) is much easier, but the API looks odd to a py3-only programmer.
After writing this message, I see that Serhiy wrote a patch to do this.

2) is an api change that perhaps should have happened in 3.0. Deprecation is 
awkward since people should not change from, for instance, self.iterkeys to 
self.key, until the api change in made.

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nosy: +terry.reedy

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[issue20729] mailbox.Mailbox does odd hasattr() check

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

Actually it should be iteritems(). This is meant to support Mailbox, which has 
both iteritems() and items() methods. iteritems() returns an iterator and 
items() returns a list. Looks as changeset f340cb045bf9 was incorrectly applied 
to mailbox. Here is a patch which partially reverts changeset f340cb045bf9 for 
the mailbox module and fixes tests in 3.x.

Perhaps we should change items() to return an iterator in Python 4.0.

--
components: +Library (Lib)
keywords: +patch
nosy: +barry, petri.lehtinen, r.david.murray, serhiy.storchaka
stage:  -> patch review
type:  -> behavior
versions: +Python 3.3, Python 3.4
Added file: http://bugs.python.org/file34189/mailbox_iters.patch

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[issue20729] mailbox.Mailbox does odd hasattr() check

[Chris Angelico]

New submission from Chris Angelico:

Only noticed because I was searching the stdlib for hasattr calls, but in 
mailbox.Mailbox.update(), a check is done thus:

if hasattr(arg, 'iteritems'):
source = arg.items()
elif hasattr(arg, 'items'):
source = arg.items()
else:
source = arg

If this is meant to support Python 2, it should probably use iteritems() in the 
first branch, but for Python 3, it's probably simpler to just drop the first 
check altogether:

if hasattr(arg, 'items'):
source = arg.items()
else:
source = arg

Or possibly switch to EAFP:

try:
source = arg.items()
except AttributeError:
source = arg

--
messages: 211920
nosy: Rosuav
priority: normal
severity: normal
status: open
title: mailbox.Mailbox does odd hasattr() check

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